Magnetron tube magnet structure



1958 T. A. HADDAD MAGNETRON TUBE MAGNET STRUCTURE Filed March 15, 1956 //Y/ lgk D A Aw 0A H N. Y WA E N IR w 0 T w T E W H T 6 Y B United States Patent 2849645 MAGNETRGN MAGNET STRUCTURE Theodore A. Haddad,.Swarthmore, .Pa.,.ass'iguor to Burroughs Corporation, Detroit, Mich, a corporation or Michigan I Application March 15, 1956, Serial;No.l-571',-649 7'Claims. (Cl.315- 8) This invention relates to .a plurality .of magnetron tubes operating in close proximity and more particularly concerns a plurality of magnetron beam switching tubes in a structure enabling their stable toperationlin a closeproximity cluster.

Magnetron beam switching tubes are most conveniently and economically provided with the necessary axial magnetic field by enclosingithe tube elements and their envelope in a cylindrical permanent :magnetwhich'maintains flux through the .tube along :lines .parallel to the tubes axis. With -such:a uniformadistribution:ofmagnet structure around the tube, this imagneticlfield issubstantially uniform in athe area occupied by :tube electrodes. Further, any slight variation :in field strength is symmetrical about the was not :the ztube .so that the behaviorof all beam-holding positions around the tube are the same with respect ;to :static :beam holding and dynamic beam switching 01' :forming. Tube .operation is .aifected by disturbance of this :ma-gnetic :fieldis :axial alignment and-symmetry.

When it is attempted to operate-such magnetaencased tubes in close proximity to .each .other, :they .cease to operatevreliably at-separations lessxthan about fourinches between centers. The respectivezm'agneticifieldsinteract upon each other, disturbing their axial .alignment and upsetting their axial symmetry toaseriOusid'egree. :This has imposed a serious handicap upon vuseof.magnetron beam tubes in compact clusters .of a :plurality :of such tubes.

An important object of :this invention is :to provide :a magnetic structure associatedwvith la t-pluralityaof :magnetrons and enablingtheir stable operationn'n accompact cluster. I

a Another important object of this invention .is -to 1pr0- 'vide a-low reluctance magnetic structure dbetweenrpairsof a;plurality of magnetrons .to .control magnetic field patterns and :enable each tube'tofunction reliably while in close proximity to other-tubes.of the plurality.

In accordance with this invention there are provided bars' of low reluctance, high permeability material rhaving low residual magnetism, interposed :between adjacent cylindricalmagnets of magnetron beamtswitching'tuhes at theirpoints of nearest proximity, conducting the .i-external magnetic fields of'these magnetswso asito prevent interaction between 'the respective :magnetic Efields.

For a=-more detailed understanding of this iinvention reference is made to :the drawings. in which:

Fig. 1 is a perspective iview of a ;pair;of=.magnetron beam switching tubes *withsv a low reluctance flmetallic Rbar between them;

Fig. .2 is a schematic representation of .the magnetic flux lines of a cylindrical magnetisuch as vused ion a magnetron beam switching tube;

Fig. 3 is a schematic represent-ationot the magnetic flux lines of two-cylindrical magnetscin close proximity;

Fig. 4 is a schematic representation of the magnetic flux lines of .two cylindrical magnets in close proximity, with a low reluctance memberinterposed; and

' .tion ,of tube 20, magnet .21 has Batented Aug. 26, 1958 .Fig. 15 is a .plan view .of acluster of magnetron tubes with interposed low-reluctance members .to permit close proximity within'the. cluster.

The .magnetron beam switching .tubes as shown in Fig. :1 are as described and claimed .in United States Patent No. 2,721,955, issued to Sin-pih2Fan.and'-Sau1 Kuchinsky aentitled ",Multi-Position LBEBHI Tube. By use of the crossed :electric and magnetic :fields of va magnetron .type structure and .of .a numberiof electrodes in .successive:arrays around a cathode, this :tubecan provide aihigh-current.electron beam to arplurality of.output electrodes 'in :rapid' succession and with great .relia'bility.

.As shown in :Fig. 1, .a cylindrical magnet 21 :encloses tube .20 and provides an axial magnetic :field Etherethrough. Tube 20 contains a .central :axial cathode 22 surrounded by several xconcentric arrays of electrodes. 0n aicircularclocusnearest to :thecathode are.the beam forming and )hdlding .electrodes 23, called spade electrodes. zBeyondthe-spade electrodes on another circular locus are the target electrodes 24,:positioned peripherally.on .thisrcircle so as .to cover;therinter-spade spaces and torcollect beamacurrent flowing :into such spaces 'between spades. intermediate between one-edge of each spade and Lthfi lnear edgei of each target proximate :to that spade are .the switching tgrid .electrodes 25. These grids also are ion a circular locus centered .ufllthe cathode .22.

With the cathode heated :to electron emission .temperature .and azpositivepotential onthe spade :electrodes and :target electrodes, the magnetic field from magnet 21sis above that tvalue required for magnetron type 'cutoff. oftcurrent-inathe tube and .no currentwill'fiow. However, lif one vof the spade electrodes .is .reduced tin .potential to about half its previous potential the voltage gradients within the tube are .distortedand ajbeam .will form. This electron beam;grazes;the low potential spade and strikes the adjacent .targetelectrode. A small portion of jtheelectron beam does'flowio this spade. .With a suitable :series resistor interposed .in the connection of'each spade -to its positive voltage supply, .this small portiomofthe beam current producesian IR drop :Which enables thezspadeito hold the .beam stablyin place once itgrazes ;that spade.

Switching grid electrodes 25 upset this stable be-am holding condition when .a suitable .negative potential is applied tto the grid which .is till the same :inter-spade Space as is the beam. As .this grid goes :negative, the beam -fans outacross the target electrode .and some of it strikes .the next "spade ABIeQtI OdC- :This fraction of beam current produces another IR voltage .drop which lowers the potentialof'this nextspade. With .aalowered Potential on the-next :spade, the beam switches over to thenext target. Thisswitchingaction occurs at every rapid irate, the ztime required to a switch from one :target to the next beingin tthesorderrof one-tenthof a microsecond.

When two-tubes 20 :and zflfltpositioned on a common surface such as a chassis, are brought :any closer .than a .tewiinches between centers, ;-aboutthreeor four inches, without the precautions prescribed by the present invention, they cease to be capable of reliable operation. However, interposition of low reluctance-bar 30 permits reliable operation .even with magnets ,21 and :21 so close ;as.to contact bar 3.0. Bar 30.controls ,theteX-ternal fields of magnets .21 and 211 to prevent interaction, as will be described.

In Figs. 2, 3 and 4, the detailsofenvelope 26:and tube electrodes .22 .,to ,25 are not shown, inasmuch as they .do not,mate,rially .atfect the magnetic fieldpf magnet }21 which surrounds .them.

To achievethe needed innermagneticfield 'for;op eraan overall magnetic field as shown in Fig. 2 with lines of force centered about the tube electrode axis. With the electrodes of tube 20 assembled for clockwise beam advancement, and correspondingly for counter clockwise motion of electrons within the beam and in the cathode-to-anode space, when seen in top plan view, it is imperative that each tubes cylindrical magnet 21 be positioned to present its south pole at the top and its north pole at the bottom of the cylinder.

When two tubes and their magnets 21 and 21 are brought into close proximity as shown in Fig. 3, their magnetic fields interact. Similar magnetic poles are being brought close together, so the flux lines from adjacent magnets repel each other. The two south poles at the top of adjacent magnets are receiving fiux lines which have come from the north poles at the bottom of the magnets. These flux lines are flowing in the same direction and are mutually repulsive. This repulsion forces each magnets flux lines in a direction away from the adjacent magnet, thereby distorting the inner magnetic field so that the lines of force are not centered within the tube, thereby making it unsuitable for operation of the magnetron beam switching tube. The closer magnets 21 and 21 are brought to each other, the more pronounced this distortion becomes. With usual field strengths and at a center-to-center separation of about 3 to 4 inches, this distortion causes the enclosed tubes to become inoperative. A center-to-center spacing greater than about 4 inches produces an unduly bulky assembly when several tubes are to be used, imposing a serious operating limitation upon multiple-tube applications.

Extensive exeriments were performed to determine equipment and apparatus which could be used to permit operation of magnetron beam switching tubes in close proximity. When a bar 30 of iron was interposed between magnets as shown in Fig. 2, it was found that the external fields of magnets 21 and 21 were substantially confined to the low reluctance path through bar 30 and did not interact upon each others internal field to any significant extent. As seen in Fig. 4, bar 30 achieves a shielding effect, in that flux lines are by-passed through it and do not extend as they do when bar 30 is absent. With bar 30 interposed, the internal magnetic field within magnets 21 and 21' are substantially the same as in an isolated magnet, as in Fig. 2; and the enclosed tubes function normally even though they are as close together as dimensions of magnets and bar will permit.

Clusters of more than two tubes also can be provided, as shown in Fig. 5. Bars 30 to 36 of low reluctance material such as iron or steel are interposed between magnets 21, 21, etc., along the lines between tube centers. In addition to the configuration shown, other cluster configurations can be used to take advantage of available space or to meet particular design requirements. Tube centers could be aligned along lines parallel to rectangular coordinates, along a ring, or following a helix or in other geometric patterns, and still utilize this means for keeping a close spacing between tubes.

The dimensions of bar 30 are not critical. A bar of cold rolled steel A x /2" x 1% was found to give satisfactory results, and could vary from this size by a considerable percentage with no change in results. Other low reluctance, high permeability materials also can be used for bar 30.

There is thus provided a low reluctance by-pass or shield between magnetron beam switching tubes, preventing interaction of magnetic fields and permitting reliable operation of a plurality of such tubes, in close proximity.

What is claimed is:

1. A magnet structure for a plurality of magnetron tubes comprising a plurality of cylindrical magnets positioned in proximity on a common surface with their magnetic axes mutually parallel, and a plurality of bars of low reluctance material interposed one between each pair of adjacent magnet walls of said cylindrical magnets with the major axes of said bars parallel to said magnetic axes.

2. A magnet structure for a plurality of magnetron tubes comprising a plurality of tubular magnets of substantially the same length positioned in close proximity with their magnetic axes mutually parallel and their magnetic poles in a common alignment, and a plurality of bars having one major axis of low magnetic reluctance material substantially coextensive with said cylindrical magnets and interposed between and in contact with adjacent walls of said cylindrical magnets with the major axes of said bars parallel to said magnetic axes.

3. A geometrically arranged cluster of magnetron beam switching tubes including a cylindrical magnet surrounding each tube and positioned in proximity to each other and in a common alignment, and a plurality of elongated ferro-magnetic bars interposed between adjacent tubes and substantially parallel with the magnetic axis of said cluster of tubes.

4. A compact cluster of magnetron beam switching tubes including similar cylindrical magnets surrounding each tube and positioned in a common magnetic field orientation and polarity, and a plurality of ferromag netic bars of substantially the same length and the same thickness as said cylindrical magnet walls interposed between and in contact with adjacent walls thereof.

5. A cluster of vacuum tubes, each tube having an elongated central cathode and concentric arrays of electrodes in an evacuated envelope and a cylindrical magnet coaxially aligned with said cathode to produce a magnetic field parallel to and Symmetrical about said cathode, with each tube of said cluster positioned in such proximity to another tube as to be within the external portions of the magnetic fields of that other tube whereby said external portions destroy the symmetry of the magnetic field about each tubes cathode, and a low reluctance member positioned between adjacent magnets to bypass said external portions of their magnetic field to thereby maintain the symmetry of each magnetic field about its respective cathode.

6. A magnet structure for a plurality of magnetron tubes comprising a plurality of hollow cylindrical magnets oriented in a common polarity and positioned on a common surface and in a compact cluster, wherein their magnetic fields are mutually disturbing so as to destroy the magnetic field distribution needed for operation of said magnetron tubes, and a plurality of low reluctance members having a length substantially the same as said cylindrical magnets and a thickness about the same as the walls of said magnets and a width less than their length, interposed between and in contact with i said cylindrical magnets at their points of nearest approach to bypass the portions of said magnetic fields which are mutually disturbing.

7. A cluster of vacuum tubes, each tube having an elongated central cathode and concentric arrays of electrodes in an evacuated envelope and a cylindrical magnet coaxially aligned with said cathode to produce a magnetic field parallel to and symmetrical about said cathode, with each tube of said cluster positioned in such proximity to other tubes as to be within the external portions of the magnetic fields of said other tubes whereby said external portions destroy the symmetry of the magnetic field about each tubes cathode, and a plurality of low reluctance members positioned between adjacent magnets to bypass said external portions of their magnetic field and thereby restore the symmetry of each magnetic field about its respective cathode.

References Cited in the file of this patent UNITED STATES PATENTS 2,014,532 Koch Sept. 17, 1935 2,292,161 Roosenstein Aug. 4, 1942 2,591,997 Backmark Apr. 8, 1952 

